oracle size of tables in schema

1-- Oracle: Size of a table in a tablespace
2SELECT
3    e.owner,
4    e.segment_name,
5    e.tablespace_name,
6    SUM(e.bytes) / 1048576 megs
7FROM dba_extents e
8WHERE
9    e.owner = 'xxMY_OWNERxx'
10    AND e.tablespace_name = 'xxMY_TBSxx'
11    AND e.segment_name = 'xxMY_TABLExx'
12GROUP BY e.owner, e.segment_name, e.tablespace_name
13ORDER BY
14    e.tablespace_name,
15    e.segment_name;